The present invention relates to tools used in the drilling and completion of oil wells. In particular, the invention relates to a tool that can be used to reduce friction between a liner and a well bore during run in or to release a drill string prior to its removal from a well bore.
In the drilling of oil wells, a drill string and attached drill bit are used in conjunction with a flow of drilling mud to drill a well hole. After the well hole is drilled, the drill bit and drill string is removed and a casing or a liner may be run in (removably attached to a drill string) across the productive interval. With the casing or liner in place, cement slurry is pumped down through the drill pipe, through the liner or casing and into an annulus between the liner or casing and the well hole wall to set, cementing the liner or casing in place and keeping production fluids in the liner or casing.
Quite often, wells are not completely vertical. They can have substantial horizontal components. Wells with long portions having a substantial horizontal component are called high angle, extended reach wells. Running the liner through high angle, extended reach well holes can be difficult because of friction between the liner and the well hole wall caused by the weight of the liner against a nearly horizontal wall. Translational friction can be substantially reduced if the liner can be rotated while fluid is flowing and it is being run into the well hole.
Conventional tools to run liners into extended reach well holes have not been able to rotate the liners while they were being run in, although some tools permit rotation after run in and during cementing. However, these rotation permitting tools do not allow fluid (e.g., drilling muds or cement slurry) flow past the tool. Another reason for this lack of run in rotation is that one direction of rotation is conventionally used to release the run in tool from the liner once the liner is in place. Rotating may therefore cause the conventional connections to release. Consequently, it has not been generally possible to rotate the liner in either direction to reduce frictional drag during run in.
Sometimes during the drilling of a well, a drill string has to be pulled from the well hole because something in the leading end of the string gets stuck. To pull the main string portion may require disconnecting it from the stuck portion. Typical, the disconnection is done by applying left hand torque to the drill string in order to unscrew a connection at some arbitrary point within the drill pipe, if connection is not over-torqued. Thus, left hand rotation and excessive right hand torque is avoided during drilling.